In recent years, there has been a growing demand in battery chargers for handheld electronic devices such as digital cameras, digital camcorders, PDAs, MP3 players, etc. Due to the increasing functionalities of these electronic devices, the battery capacity has also been increasing accordingly. The proliferation of portable electronic devices has greatly increased the need for various types of charging schemes by which the portable electronic devices may be charged. The use of linear charging techniques, where an isolated AC to DC converter followed by a linear regulator is used (often to as a two-pass scheme) to charge the battery of the portable electronic device has become difficult to accommodate due to the high charging current requirements. In an AC to DC converter, the adapter is plugged in to the portable electronic device to enable charging of the battery therein.
Another type of charging device has utilized a one-pass charging scheme where the AC to DC converter directly charges the battery without a linear regulator. In this configuration, the portable electronic devices are placed within a cradle configured to receive the portable electronic device, and the battery is charged via some type of inductive coupling. In one-pass charging configurations a primary side of a transformer is included within the cradle charger and a secondary side of a transformer is normally associated with the portable electronic device including the battery being charged. Alternatively, the charging circuitry is contained in the cradle and a battery is placed therein.
Charging current requirements on the secondary side of a cradle charger or in linear charging techniques are often benefited by a direct control method on the secondary side of the AC to DC converter due to the fact that this control method is not restricted to the charging current and provides lower costs. A secondary side IC control may be used to control the charging operations for some portable electronic devices. The secondary side IC control is currently available within the marketplace but cannot address the issue of charging a dead or fully discharged battery. This is due to the fact that the IC controller needs a minimum bias voltage in order to function. The bias voltage is determined by the battery charging voltage of the portable electronic device. Thus, when the battery is completely discharged and a charging is attempted, the IC controller will not obtain adequate bias voltage and will not be able to function in a normal manner. Thus, some manner for enabling better control on the secondary side of a cradle charger controller when the battery of a portable electronic device is fully discharged would be greatly beneficial.